The possibility of increasing the laser pumping efficiency of a flashlamp by recycling flashlamp radiation below a certain wavelength has been discussed theoretically by V. M. Gardashyan et al, Soviet Jour. Quant. Elektr. 1 296 (1971), and by I. I. Litvinov et al, Soviet Jour. Quant. Elektr. 4 131 (1974) and has been examined experimentally for one situation by S. A. Baranov et al, Soviet Jour. Quant. Elektr. 8 102 (1978). However, no published work has appeared on control of thermal load generated in a solid state matrix of a laser, or on joint control of pumping efficiency and thermal load generation, through use of wavelength-selective coatings on the flashlamp envelope. The subject invention achieves such control or joint control.
A laser flashtube, discussed briefly by Karney in U.S. Pat. No. 3,582,822, uses a wavelength-selective coating on a flashlamp/laser rod window to admit only higher wavelength radiation to enhance absorption of the transmitted flashlamp radiation by the narrow pump bands of the laser rod material. No quantitative data are given in support of the approach, and the tradeoff between laser rod pumping and laser rod heating (at adjacent wavelengths) is not discussed.
Crow, in U.S. Pat. No. 3,634,779, discloses use of an impregnated flashlamp jacket and uv-absorbing filter that is positioned within the laser rod material to suppress transverse radiative emissions at the laser wavelength; this suppresses depumping of the inverted quantum population within the rod. A second, similar filter may be positioned between the laser rod and the flashlamp; and a third filter may be positioned within the flashlamp jacket material to absorb radiation at uv. and lower wavelengths. Recycling of radiation in specified wavelength ranges within the flashlamp itself is not discussed or, apparently, even contemplated.
U.S. Pat. No. 4,039,970, issued to Shiroki, Mori and Kuwano, discloses use of a radiation filter that absorbs all wavelengths .lambda.&lt;5000 .ANG., positioned between the initial radiative source and the laser material to be pumped. The removal, rather than recycling, of all flashlamp radiation of wavelengths below .lambda.=4,500-5,000 .ANG. decreases the input energy required to reach laser oscillation threshold (approximately 1.1 Joules for a YAlO.sub.3 crystal) and increases the laser output energy for a fixed input of about 10 Joules.
Broadt, in U.S. Pat. No. 4,399,490, discloses the use of suitable electromagnetic radiation reflectors, backed by opaque, radiation-absorbing materials, to substantially reduce the back radiation from a flashlamp reflector. This approach seeks to suppress transmission of electromagnetic radiation at all wavelengths rather than to recycle radiation in selected wavelength ranges.